1. Field of the Invention
The present invention relates to an inkjet recording apparatus and method, and an abnormal nozzle determination method, and in particular to technology for determining ejection defects (flight deviation, droplet volume abnormality, splashing, ejection failure and the like) occurring in an inkjet head having a plurality of nozzles (droplet ejection ports), and to correction technology for suppressing decline in image quality arising from nozzles having an abnormality.
2. Description of the Related Art
An inkjet apparatus which forms images by ejecting a functional material (hereinafter, taken to be synonymous with “ink”) using an inkjet head, has the following characteristic features: excellent eco-friendly properties, capability for high-speed recording on various different recording media, the capability to achieve high-definition images which are not liable to bleeding.
However, in recording by an inkjet method, ejection defects occur with a uniform probability in the nozzles of the head, and stripe non-uniformities and density non-uniformities occur at image positions corresponding to the defect nozzles.
As a result of this, image quality is impaired, and maintenance and correction must be carried out each time an ejection defect occurs, leading to a decline in through-put and increase in wasted paper.
In particular, in a single-pass method which performs image formation by means of one recording scan, an ejection defect in one nozzle has a great effect on the overall image quality. Furthermore, in the case of an inkjet printer based on a single-pass method which places emphasis on through-put, since the recording head (inkjet head) is always situated over the recording medium, then it is difficult to carry out head maintenance during an image forming operation and hence the effects of an ejection defect are great.
Possible causes of the occurrence of ejection defects in an inkjet head are: decline in ejection force due to air bubbles which have mixed into the nozzles, adherence of foreign matter to the vicinity of the nozzles, abnormality in the lyophobic properties in the vicinity of the nozzles, abnormality in the nozzle shape, and the like. Moreover, a nozzle which has produced an ejection defect is liable to create an ink mist due to instable ejection, and this mist causes deterioration of the surrounding nozzles which are functioning normally.
Japanese Patent Application Publication No. 2008-093994 discloses a composition in which, as a device for accurately detecting defects on a nozzle surface, when inspecting a nozzle surface, in each period of one droplet ejection operation, droplets are ejected from the nozzles after causing liquid to overflow onto the outside of the nozzles and causing liquid to adhere to the nozzle surface.
Furthermore, as a method for previously detecting nozzles which are liable to give rise to ejection defects, Japanese Patent Application Publication No. 2003-205623 describes performing ejection failure nozzle detection at a maintenance position outside an image formation region by using a waveform that is different from a recording waveform, and carrying out maintenance in cases where an ejection failure has been detected.
Japanese Patent Application Publication No. 11-348246 describes technology for determining nozzles which are ejecting abnormally and performing correction by means of the surrounding nozzles which are operating normally.